1. Field of the Invention
The present invention generally relates to a liquid jet recording apparatus and, more particularly, to a liquid jet recording apparatus using a recording composition where fine particles are dispersed.
2. Description of the Related Art
Recently much attention has been paid to a non-impact recording technology because the noise caused by its recording operation can be reduced to an almost negligible degree. Among this technology, an ink-jet recording method, which is capable of high-speed recording, is a promising candidate, and its operation can be performed using a plain paper without a special fixing process. In this field, various approaches for practical use have been proposed including those already commercialized and others still in the development stage.
Such an ink-jet recording method, where droplets of a recording composition, usually called ink, produces a recording image on a record receiving member by flying droplets of a recording composition directly onto a surface of the record receiving member. This recording system can be classified into several processes according to the methods of generating the droplets and controlling the flight direction of the droplets.
In the prior art, for example in U.S. Pat. No. 3,060,429, it is known that a Teletype process, which is an electrostatic attraction type process, provides a generation of droplets of a recording composition by electrostatic pull, and the resulting droplets can be controlled by an electrical field according to recording signals to place the droplets on a surface of a record receiving member selectively to achieve a recording.
U.S. Pat. Nos. 3,596,275 and 3,298,030 describe a Sweet process which is a continuous stream and charge-controlled type process, in which droplets can be generated by a continuous vibration method, with an electrostatically controlled charge, and then the droplets pass between a pair of electrostatic deflecting electrodes with a uniform electric field to deposit the droplets on a surface of a record receiving member, thus producing a recording image.
As another method, for example, U.S. Pat. No. 3,416,153 teaches a Hertz process, in which an electric voltage is applied between a nozzle and a ring-shaped electrode near the front of the nozzle to generate a mist of liquid droplets by continuous vibration to obtain a recording image on a recording member. That is to say, in this process a strength of the electric field applied between the nozzle and the electrode can be modulated in accordance with recording signals to control a mist state of the droplets, thereby creating a gradation in the recording image.
Moreover, as another method, for example, U.S. Pat. No. 3,747,120 discloses a Stemme process. A principle of this process is fundamentally different from that used in the above three processes. That is, while all the above three processes employ electrical control of the droplets emitted from the nozzle during the flight from the nozzle to place the droplets corresponding to the recording signals on the surface of the record receiving member selectively, in this Stemme process the droplets can be emitted directly from the nozzle to a receiver only when they are required for recording. In other words, in the Stemme process, electrical recording signals can be applied to a piezo vibrating element which is attached to a recording head with the nozzle, in which the recording liquid can be emitted, to convert the electrical signals to a mechanical vibration of the piezo element. The droplets can be emitted from the nozzle according to the mechanical vibration, thereby forming a recording image on the record receiving member. This process is called a drop-on-demand type.
Furthermore, Japanese Patent Publication 56-9429 discloses still another process previously proposed by the present applicants. This process also employs the so-called drop-on-demand method which emits and flies droplets of a recording composition from the nozzle according to recording signals. This process is a so-called bubble-jet method where ink droplets can be ejected from the nozzle by an action of a vapor bubble in an ink generated by heating the ink in an ink chamber.
As noted above, although the ink-jet recording method has various processes on the basis of the principle, there is a common point between these processes, in which common point droplets of a recording composition, generally called ink, are emitted to form the recording image on the record receiving member. Such ink is generally an aqueous recording liquid wherein a water-soluble dye is dissolved. Recently, however, due to a strong need for water and light resistances in recorded images, it has been anticipated that a pigment-based ink with a strong image durability will be used as a color agent for the recording composition of ink-jet recording ink. For example, aqueous pigment-based inks for ink-jet recording ink which meet a basic demand for recording quality, ejection characteristics, storage stability, penetration and absorption properties into a recording medium and the like, are described in Japanese Laid-Open Publications 2-255875, 4-57859, and 4-57860. However, the pigment-based inks described in the above publications have an inherent disadvantage of particle dispersion instability in a liquid medium, unlike the dye which can be dissolved in the liquid medium stably, thus creating problems, such as pigment aggregation, sedimentation, separation in the recording liquid and thereby nozzle clogging which plague ink-jet recording technology.
On the other hand, to obtain a high-quality and high-resolution ink-jet recording image, a smaller nozzle has been required for this purpose, although a conventional nozzle diameter from xcfx8633xcx9cxcfx8634 xcexcm (about 900 xcexcm2 in terms of cross-sectional area of a nozzle orifice) to xcfx8650xcx9cxcfx8651 xcexcm (about 2000 xcexcm2 in terms of cross-sectional area of the nozzle orifice) in a recording head has been used. In this case, when the recording composition wherein the aqueous dye can be dissolved is used as an ink-jet ink, the problem of nozzle clogging is resolved because the dye is dissolved completely in the liquid medium. For the pigment-based ink, however, there has been a serious problem of nozzle clogging in a recording operation with the smaller nozzle having, for example, a nozzle diameter of less than xcfx8625 xcexcm.
Furthermore, the above recording composition including the pigments can cause an ink passageway of the ink-jet recording head to be cut away and damaged due to a long time operation, in the same way that a mountain can be eroded by river water including small pebbles. Although it is not a problem when only the ink passageway is subjected to slight damage and wear, damage and wear of the orifice of the nozzle lead to serious degradation of ink drop ejection characteristics.
Especially, because a smaller ink drop volume is required to achieve a high-quality and high-resolution ink-jet recording image in the ink-jet recording method, the nozzle diameter of the recording head has become increasingly small. For example, the nozzle diameter has become less than xcfx8625 xcexcm, or less than 500 xcexcm2 in terms of cross-sectional area of the nozzle orifice, although the conventional diameter from xcfx8633xcx9cxcfx8634 xcexcm (about 900 xcexcm2 in terms of cross-sectional area of the nozzle orifice) to xcfx8650xcx9c51 xcexcm (about 2000 xcexcm2 in terms of cross-sectional area of the nozzle orifice) of the recording head nozzle has been successfully used. In the conventional case, since the previous relatively large nozzle is subjected to little damage and wear, there is little influence on ink droplet ejection characteristics, such as ejection stability, ink weight uniformity and the like, thus introducing no problem. However in the case of the smaller nozzle having, for example, a diameter less than xcfx8625 xcexcm, even a little damage and wear have significant influences on ink droplet ejection characteristics, thereby introducing a serious problem.
It is an object of the present invention to provide a liquid jet recording apparatus eliminating the nozzle clogging problem, in which a recording composition formed by dispersing fine particles in the liquid is ejected from a small orifice of a nozzle to place ink droplets on a receiver medium, thus producing a recording image. Above all, the present apparatus is to provide no nozzle clogging problem, yet produce an excellent high-resolution recording, having water and light resistances for recorded images using a nozzle diameter of less than xcfx8625 xcexcm (less than 500 xcexcm2 in terms of cross-sectional area of a nozzle orifice).
To accomplish the above objects, there is provided, in accordance with the present invention, a liquid jet recording apparatus wherein a recording composition satisfies a relationship 0.001xe2x89xa6Dp/Doxe2x89xa60.01, where Dp is a size of a fine particle, and Do is a diameter of a fine nozzle orifice, on the condition that the diameter of the nozzle orifice is less than xcfx8625 xcexcm. According to the present invention, a high-quality recording with high water and light resistances can be realized and a reliability of an ink-jet recording apparatus can be improved with the absence of nozzle clogging in the present recording apparatus.
The problem of nozzle clogging in the present apparatus can be eliminated completely under the conditions that a content of the fine particles in the recording composition is in the range of 2 to 10% by weight based on the total amount of the recording composition, and that a solid content of the recording composition including the fine particles is less than 15% by weight, when the diameter of the nozzle orifice in the present apparatus is less than xcfx8625 xcexcm. According to the present invention, a sufficient ink density for practical use and a stable dispersion of fine particles can be obtained because of optimization of the content of the fine particles in the recording composition and the solid content of the ink, and a recorded image with high water and light resistances can be realized with the absence of nozzle clogging in the present recording apparatus.
The problem of nozzle clogging in the present apparatus can be prevented completely under the requirement that Dp/txe2x89xa60.01, wherein the diameter of the nozzle orifice is less than xcfx8625 xcexcm, and t is a length of the orifice having a uniform cross-sectional area at an outlet portion in the nozzle. According to the present invention, a high-quality and high-resolution recording image can be obtained with the absence of nozzle clogging, thereby improving a reliability of the apparatus.
A high-quality printed image by use of the present apparatus can be accomplished by maintaining a distance of less than 100 t from the orifice of the nozzle to a receiving medium and ejecting ink droplets in a direction of gravity.
Damage and wear of the nozzle formed of a resin in the present apparatus can be prevented by making a hardness of the resin within a range of Rockwell M65 to M120. According to the present invention, a stable high-quality recording can be realized with no deterioration of the ink ejection characteristic due to nozzle damage and wear.